How can a computer create random numbers?

I wonder, how it is possible for computers to generate random numbers. Normally, I would think, as a layman, that a computer always works exact and accurate and a mathematical function always provides a predictable result. So, where are the numbers from the random number generator coming from?

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Guest

There are different ways, how a computer can proceed. First, there are so-called pseudo-random number generators. They just use a list of previous defined random numbers from which just a number is selected. Of course, that is not truly random and there is the problem, that the numbers forcibly repeat sometime, depending, of course, on the length of the list.

Better results are obtained with a different class of random number generators, which are processing certain "random" values from the computer to derive random numbers from them. This can be, for example, the computer's clock in milliseconds, that is constantly changing, or the moving of the mouse, or the noise of a sound input or a card attached to the computer. The resulting values are relatively unpredictable and thus lead to very good results, which look pretty random, after being chased by a corresponding function.

To test how good a random function is, it can be called a million times, to then look at the distribution of the output values. Here, the distribution should be quite equal and there should occur no unexpected spikes or depressions at certain values.05/01/2012 at 19:59

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Computer Expert

There are mathematical functions that already vary enormously with small changes in the values of the parameters. If you put in these functions, for example, the system time as an initial value, quickly the whole range of values is uniformly covered and we get our random number by scaling to the desired range.06/01/2012 at 21:34

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